This application is related to drive systems for zero turn radius (ZT) vehicles. In the past, such drive systems have utilized separate hydraulic pump and wheel motor combinations under individual left and right side control. Such an arrangement permitted the left and right side drive wheels to be rotated in opposite directions to execute zero radius turns about a central point. More recently, integrated transaxles having a hydraulic pump and motor, axle and/or reduction mechanism in a single housing have been used to replace the traditional pump and wheel motor combinations in ZT vehicles. These integrated transaxles have an economy of space and eliminate external closed-loop hydraulic lines. In each of these cases, a prime mover such as an internal combustion engine or electric motor powers the input shafts of the left and right side drive mechanisms through one or more belt and pulley arrangements, leading to some duplication of drive system components.
Most recently, integrated drive mechanisms have been introduced in which the independent left and right side drive mechanisms are combined to form a single drive unit having a central input shaft driven by the prime mover, whether indirectly by belt and pulley arrangement or directly by coupled shaft. Such an arrangement eliminates duplication of the input means between the prime mover and the left and right side drive mechanisms. Typically, the drive mechanisms are hydraulic, but alternative drive mechanisms such as toroidal drives have been used to motivate ZT vehicles. Integrated drive units featuring these various drive mechanisms will have unique design requirements. The rigid structures of such integrated drive units, because they typically span the width of a ZT vehicle's frame, are subject to various loads including torsional loads as the vehicle's frame twists and flexes during severe operation. There exists the need to have a more flexible drive apparatus, one that communicates with the prime mover through a central input shaft, and one that is capable of encompassing a host of drive and output options.